1. Field of the Invention
This technology relates to oil and gas wells, and in particular to seals in gate valves used in oil and gas field applications.
2. Brief Description of Related Art
Typical gate valves used in connection with oil and gas operations have a valve body with a flow passageway that extends therethrough. The flow passageway intersects a central cavity, where a gate is located. The gate has an opening, and moves between open and closed positions. When in the open position, the opening is aligned with the fluid path so that fluid can flow therethrough. Conversely, when the gate is in the closed position, the gate blocks the flow passageway. The gate is attached to a stem, which controls the position of the gate between the open and closed positions. Typically, seat rings are placed in counterbores formed in the valve body at the intersection of the flow passageway and the cavity.
A typical gate valve may further include a bonnet that is attached to the valve body. The bonnet surrounds the stem, which passes from the central cavity through a stem opening in the bonnet. This stem opening is generally in communication with the central cavity. Accordingly, the space between the stem and the bonnet must be sealed to avoid leakage.
In addition, the seat rings generally have seat seals that seal the seat rings to the valve body. Such seat seals prevent the entry of fluid from the central cavity to the downstream flow passageway. When the gate is open, the seat seals help to keep the seats centralized in their pockets, and minimize the ingress of sand and debris into the central cavity. When the gate is closed, fluid will flow past the upstream seat ring and into the central cavity. The seat seals of the downstream seat ring prevent this fluid from passing between the downstream seat ring and the valve body into the downstream flow passageway. By positioning seat rings on either side of the gate, the gate valve can be used for bi-directional fluid flow, because no matter which way the fluid flows, there is always a seat ring having seat seals on the downstream side of the gate.
Elastomeric stem and seat seals have been used in the industry. However, since elastomeric seals do not have the necessary longevity, especially in corrosive environments, or the ability to withstand high temperatures and pressures, metal seals have become popular. Metal seals, however, have their own problems, including premature wear, damage to the sealing surfaces, and insufficient sealing capacity under certain conditions.